The present invention relates to a middle ear implant with a flat coupling body for application against the eardrum, an elongated shaft connected therewith for spanning the space in the tympanic cavity, and a shaft-connected base for application against the supporting point for the implant in the tympanic cavity.
Impaired hearing ranging up to deafness can have different pathological causes. One oft he causes typically lies in a disease-related change in or degeneration oft he small auditory bones of the ossicular chain in the middle ear, i.e., the three ossicles positioned in the tympanic cavity (Cavum tympani): the hammer, the anvil, and the stirrup.
These ossicles carry sound transmission from the eardrum via the vestibule window (vestibular window) to the inner ear, the air in the middle ear making possible almost friction-free vibration of the ossicles combined together in articulated fashion. These articulated ossicles represent a lever mechanism which amplifies the recorded sound waves in the case of humans by about two to three times. If the lever mechanism is disturbed, e.g., through a degenerative change in the bone substance, a person will become hard of-hearing.
It is known to totally or partially replace the damaged ossicular chain surgically with an implanted auditory-bone prosthesis, called a middle ear implant. This typically includes a disk-shaped coupling body for application against the eardrum, an elongated shaft connected thereto for spanning the free space in the tympanic cavity which results from the surgically removed or no longer present ossicles, and an implant shoe for broad-surface application against the supporting plate for the stirrup upon replacement of all three bones (total implant) or an implant bell for application against the stirrup (stapes) with the no longer present hammer and anvil (partial implant). The middle ear implant then completely or partially takes over the transmission of vibrations from the eardrum to the vestibule window so that the patient again attains a normal hearing capacity.
The various known middle ear implants differ essentially in their structural design and in the selection of materials.
U.S. Pat. No. 4,510,627 refers to an auditory-bone prosthesis made of a porous plastic (polyethylene) with a metallic core of high sound conductivity. The porous material is intended to serve a unifying joining of the implant to the ear drum and the supporting plate while the metallic core takes over the function of sound transmission.
Also known are middle ear implants made of ceramics. These have the disadvantage, however, of being relatively bulky and reacting rather sluggishly with a weight of about 40 mg. In addition, in the case of certain ceramics, the possibility exists for complete destruction through recurring middle ear inflammations. For this reason, DE 39 01 796 A1 provides a middle ear implant made of gold, with the disk-shaped coupling body and the base made of pure gold and a gold wire as the shaft. is It is also known from DE 42 10 235 C1 to provide a middle ear implant in which the flat coupling body for application against the eardrum is made of titanium coated with a bioactive titanium oxide layer. The shaft is made of pure gold, and the implant shoe is again made of titanium.
In all of these middle ear implants, a principal problem exists in the fact that the depth of the tympanic cavity to be bridged by the implant or a portion thereof differs from patient to patient, with the limiting condition that the precise length can only be determined for the first time during surgical intervention. An implant with a patient-specific length-adapted shaft must therefore be available very quickly.
For this purpose, the above-mentioned DE 39 01 796 A1 provides for the formation oft a curved region in the shaft, which forms a reserve length and permits adjusting the overall length of the shaft to individual circumstances during surgical intervention. However, since the middle ear implant is extremely small, the length adjustment requires a considerable degree of dexterity. Also, the stability of the adjusted shaft length is not always ensured.
As a result, a number of middle ear implants with shafts of different length are currently typically kept on hand during surgery. The implant coming closest to the individual requirements is then selected. This method has the disadvantage of a considerable logistical effort with respect to the production, storage, and maintaining a ready supply of a number of middle,ear implants with shafts of different length.
The object oft he present invention is to improve the middle ear implant described above such that adaptation oft he length of the shaft oft he middle ear implant to patient-specific requirements is possible in a simple but effective manner.
The solution to this problem is attained according to the present invention in that the elongated shaft possesses potential separation points for individual adaptation oft he length oft he shaft to the patient-specific depth oft he space oft he tympanic cavity during surgical intervention and in that the base and/or the flat coupling body is formed as of a slide-on connector part accepting the corresponding end of the shaft.
The middle ear implant of the present invention can therefore be adapted very rapidly during surgical intervention to the patient-specific depth of the space of the tympanic cavity by simply breaking off the excess length of the shaft, with the base or the flat coupling body subsequently being mounted on the free end of the shaft.
According to a first further development, the middle ear implant can be designed such that the flat coupling body is joined as one piece with the shaft, and the base, having the form of a shoe for broad-surface application against the supporting plate for the stirrup, is designed as a slide-on connector part.
In this case, the implant serves as a total prosthesis, i.e., it replaces the entire ossicular chain.
The implant shoe therefore has three functions in the case of the middle ear implant according to the present invention:
1. Through its base, it is designed to ensure broad-surface application against the supporting plate for the stirrup (stapes), i.e., to avoid tipping in order to guarantee a stable position of the middle ear implant.
2. Because of its broad base, i.e., as a result of the enlarged surface area, a lower pressure is exerted on the supporting plate.
3. It covers the broken-off edge like a cap and therefore avoids the need for refinishing the current actual separation point.
According to a second further development of the present invention, the middle ear implant is designed such that the flat coupling body is formed as a slide-on connector part while the base, in the form of a bell for application against the stirrup, is joined as one piece with the shaft. In this case, the implant serves as a partial prosthesis, i.e., replaces only the anvil and the hammer.
According to a further development of the present invention, the potential separation points are formed at a predetermined mutual distance from each other, special advantages being attained if the mutual distances of the potential separation points are constant over the extent of the shaft through specification of a modular dimension.
Such a design advantageously permits stocking two types of implants whose shaft length differs by a predetermined fraction of the repeat measurement, preferably by half oft he modular dimension. Advantageously, it is then possible to have length adaptations down to one half of the modular dimension.
All oft he parts of the middle ear implant preferably consist of titanium. Titanium is a material which is lightweight, biocompatible, and a good transmitter of sound.
At least the flat coupling body and the shoe are preferably coated with a bone-like substance, preferably hydroxylapatite. Such a construction advantageously permits very intimate joining of the implant to the eardrum and the supporting plate, with the roughening of the surface of the implant parts being necessary.
According to another refinement of the present invention, the flat coupling body is formed as a disk. The disk exhibits symmetrically distributed circular openings. Such a refinement very advantageously permits very intimate intergrowth oft he ear drum with the coupling body.
According to a further development of the present invention, the flat coupling body with attached shaft, on the one hand, and the implant shoe, on the other, are manufactured in engineering production as turned parts.
In contrast to the middle ear implants according to the state of the art cited above, which sometimes need to be manufactured via troublesome manual labor, the middle ear implant according to the present invention can be produced by machining on an automatic lathe.